Headlines - Outbreaks Linked to Recreational Water in the U.S., 2009–2010

The Centers for Disease Control and Prevention (CDC) has provided an update on recreational water-related outbreaks in the U.S. during 2009–2010. These outbreaks are defined as two or more people with the same illness, linked in time and place to exposure to recreational water or water-related chemicals that have evaporated into the air around that water. There were 81 outbreaks reported in 28 states and Puerto Rico: 24 in untreated water (lakes and oceans) and 57 (70%) in treated water (swimming pools or hot tubs). These 81 outbreaks resulted in at least 1,326 cases, including 62 hospitalizations (5%), with no deaths. The etiology was confirmed for 49 outbreaks (60%), including 27 (55%) caused by Cryptosporidium. Since its initial description in 1988, the number of outbreaks caused by this agent has increased from 0 to 40 per year (p<0.001). The causative agent varies by water type: in treated water, 24 of the 57 outbreaks (42%) were caused by Cryptosporidium, whereas in untreated water, 11 of the 24 outbreaks (46%) were caused by cyanotoxins (suspected or confirmed). In treated water, the temporal distribution was bimodal, with 25 (44%) outbreaks occurring in July–August, characterized by 23 outbreaks of acute gastroenteritis, 84% of which were caused by Cryptosporidium; and 10 outbreaks in March, 5 of which were suspected to be linked to disinfection byproducts. Outbreaks linked to hotel swimming pools tend to occur from February to April, with dermatological problems caused by Pseudomonas aeruginosa in spas. In untreated water, 20 of the 24 outbreaks occurred during the summer months (June–July–August). The CDC concludes, on the one hand, that ultraviolet light or ozone is beneficial as an additional treatment to inactivate Cryptosporidium, which is resistant to chlorine, and, on the other hand, that the importance of cyanotoxins in recreational water is likely underestimated. It also emphasizes that outbreaks in recreational water are likely underestimated. These findings suggest that attention should also be paid to Cryptosporidium in France in the event of an outbreak in a swimming pool and highlight that the eutrophication of a body of water with cyanobacterial blooms poses health risks beyond mere safety concerns (such as turbid water).